C. Grasset, K. Einarsdottir, N. Catalán, L. J. Tranvik, M. Groeneveld, J. A. Hawkes, K. Attermeyer
Photochemical degradation of dissolved organic matter (DOM) has been the subject of numerous studies; however, its regulation along the inland water continuum is still unclear. We aimed to unravel the DOM photoreactivity and concurrent DOM compositional changes across 30 boreal aquatic ecosystems including peat waters, streams, rivers, and lakes distributed along a water residence time (WRT) gradient. Samples were subjected to a standardized exposure of simulated sunlight. We measured the apparent quantum yield (AQY), which corresponds to DOM photomineralization per photon absorbed, and the compositional change in DOM at bulk and individual compound levels in the original samples and after irradiation. AQY increased with the abundance of terrestrially derived DOM and decreased at higher WRT. Additionally, the photochemical changes in both DOM optical properties and molecular composition resembled changes along the natural boreal WRT gradient at low WRT (<3 years). Accordingly, mass spectrometry revealed that the abundance of photolabile and photoproduced molecules decreased with WRT along the boreal aquatic continuum. Our study highlights the tight link between DOM composition and DOM photodegradation. We suggest that photodegradation is an important driver of DOM composition change in waters with low WRT, where DOM is highly photoreactive.
溶解有机物(DOM)的光化学降解一直是众多研究的主题;然而,其在内陆水体连续过程中的调节作用仍不清楚。我们的目的是揭示 30 个北方水生生态系统(包括沿水停留时间(WRT)梯度分布的泥炭水、溪流、河流和湖泊)中 DOM 的光活性和同时发生的 DOM 成分变化。我们对样本进行了标准化的模拟阳光照射。我们测量了表观量子产率(AQY)(相当于每吸收一个光子所产生的 DOM 光矿化度),以及原始样本和辐照后样本中 DOM 在总量和单个化合物水平上的成分变化。AQY 随陆源 DOM 丰度的增加而增加,在 WRT 较高时则减少。此外,在低 WRT(3 年)时,DOM 光学特性和分子组成的光化学变化与沿自然北方 WRT 梯度的变化相似。因此,质谱分析表明,随着北方水生连续体的 WRT 下降,光吸收和光生成分子的丰度也随之下降。我们的研究强调了 DOM 成分与 DOM 光降解之间的密切联系。我们认为,光降解是低 WRT 水域 DOM 成分变化的一个重要驱动因素,在低 WRT 水域 DOM 具有很强的光反应活性。
{"title":"Decreasing Photoreactivity and Concurrent Change in Dissolved Organic Matter Composition With Increasing Inland Water Residence Time","authors":"C. Grasset, K. Einarsdottir, N. Catalán, L. J. Tranvik, M. Groeneveld, J. A. Hawkes, K. Attermeyer","doi":"10.1029/2023GB007989","DOIUrl":"https://doi.org/10.1029/2023GB007989","url":null,"abstract":"<p>Photochemical degradation of dissolved organic matter (DOM) has been the subject of numerous studies; however, its regulation along the inland water continuum is still unclear. We aimed to unravel the DOM photoreactivity and concurrent DOM compositional changes across 30 boreal aquatic ecosystems including peat waters, streams, rivers, and lakes distributed along a water residence time (WRT) gradient. Samples were subjected to a standardized exposure of simulated sunlight. We measured the apparent quantum yield (AQY), which corresponds to DOM photomineralization per photon absorbed, and the compositional change in DOM at bulk and individual compound levels in the original samples and after irradiation. AQY increased with the abundance of terrestrially derived DOM and decreased at higher WRT. Additionally, the photochemical changes in both DOM optical properties and molecular composition resembled changes along the natural boreal WRT gradient at low WRT (<3 years). Accordingly, mass spectrometry revealed that the abundance of photolabile and photoproduced molecules decreased with WRT along the boreal aquatic continuum. Our study highlights the tight link between DOM composition and DOM photodegradation. We suggest that photodegradation is an important driver of DOM composition change in waters with low WRT, where DOM is highly photoreactive.</p>","PeriodicalId":12729,"journal":{"name":"Global Biogeochemical Cycles","volume":null,"pages":null},"PeriodicalIF":5.2,"publicationDate":"2024-03-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1029/2023GB007989","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140053214","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Xuhui Wang, Yuanyi Gao, Sujong Jeong, Akihiko Ito, Ana Bastos, Benjamin Poulter, Yilong Wang, Philippe Ciais, Hanqin Tian, Wenping Yuan, Naveen Chandra, Frédéric Chevallier, Lei Fan, Songbai Hong, Ronny Lauerwald, Wei Li, Zhengyang Lin, Naiqing Pan, Prabir K. Patra, Shushi Peng, Lishan Ran, Yuxing Sang, Stephen Sitch, Maki Takashi, Rona Louise Thompson, Chenzhi Wang, Kai Wang, Tao Wang, Yi Xi, Liang Xu, Yanzi Yan, Jeongmin Yun, Yao Zhang, Yuzhong Zhang, Zhen Zhang, Bo Zheng, Feng Zhou, Shu Tao, Josep G. Canadell, Shilong Piao
East Asia (China, Japan, Koreas, and Mongolia) has been the world's economic engine over at least the past two decades, exhibiting a rapid increase in fossil fuel emissions of greenhouse gases (GHGs) and has expressed the recent ambition to achieve climate neutrality by mid-century. However, the GHG balance of its terrestrial ecosystems remains poorly constrained. Here, we present a synthesis of the three most important long-lived greenhouse gases (CO2, CH4, and N2O) budgets over East Asia during the decades of 2000s and 2010s, following a dual constraint approach. We estimate that terrestrial ecosystems in East Asia is close to neutrality of GHGs, with a magnitude of between −46.3 ± 505.9 Tg CO2eq yr−1 (the top-down approach) and −36.1 ± 207.1 Tg CO2eq yr−1 (the bottom-up approach) during 2000–2019. This net GHG sink includes a large land CO2 sink (−1229.3 ± 430.9 Tg CO2 yr−1 based on the top-down approach and −1353.8 ± 158.5 Tg CO2 yr−1 based on the bottom-up approach) being offset by biogenic CH4 and N2O emissions, predominantly coming from the agricultural sectors. Emerging data sources and modeling capacities have helped achieve agreement between the top-down and bottom-up approaches, but sizable uncertainties remain in several flux terms. For example, the reported CO2 flux from land use and land cover change varies from a net source of more than 300 Tg CO2 yr−1 to a net sink of ∼−700 Tg CO2 yr−1. Although terrestrial ecosystems over East Asia is close to GHG neutral currently, curbing agricultural GHG emissions and additional afforestation and forest managements have the potential to transform the terrestrial ecosystems into a net GHG sink, which would help in realizing East Asian countries' ambitions to achieve climate neutrality.
{"title":"The Greenhouse Gas Budget of Terrestrial Ecosystems in East Asia Since 2000","authors":"Xuhui Wang, Yuanyi Gao, Sujong Jeong, Akihiko Ito, Ana Bastos, Benjamin Poulter, Yilong Wang, Philippe Ciais, Hanqin Tian, Wenping Yuan, Naveen Chandra, Frédéric Chevallier, Lei Fan, Songbai Hong, Ronny Lauerwald, Wei Li, Zhengyang Lin, Naiqing Pan, Prabir K. Patra, Shushi Peng, Lishan Ran, Yuxing Sang, Stephen Sitch, Maki Takashi, Rona Louise Thompson, Chenzhi Wang, Kai Wang, Tao Wang, Yi Xi, Liang Xu, Yanzi Yan, Jeongmin Yun, Yao Zhang, Yuzhong Zhang, Zhen Zhang, Bo Zheng, Feng Zhou, Shu Tao, Josep G. Canadell, Shilong Piao","doi":"10.1029/2023GB007865","DOIUrl":"https://doi.org/10.1029/2023GB007865","url":null,"abstract":"<p>East Asia (China, Japan, Koreas, and Mongolia) has been the world's economic engine over at least the past two decades, exhibiting a rapid increase in fossil fuel emissions of greenhouse gases (GHGs) and has expressed the recent ambition to achieve climate neutrality by mid-century. However, the GHG balance of its terrestrial ecosystems remains poorly constrained. Here, we present a synthesis of the three most important long-lived greenhouse gases (CO<sub>2</sub>, CH<sub>4</sub>, and N<sub>2</sub>O) budgets over East Asia during the decades of 2000s and 2010s, following a dual constraint approach. We estimate that terrestrial ecosystems in East Asia is close to neutrality of GHGs, with a magnitude of between −46.3 ± 505.9 Tg CO<sub>2</sub>eq yr<sup>−1</sup> (the top-down approach) and −36.1 ± 207.1 Tg CO<sub>2</sub>eq yr<sup>−1</sup> (the bottom-up approach) during 2000–2019. This net GHG sink includes a large land CO<sub>2</sub> sink (−1229.3 ± 430.9 Tg CO<sub>2</sub> yr<sup>−1</sup> based on the top-down approach and −1353.8 ± 158.5 Tg CO<sub>2</sub> yr<sup>−1</sup> based on the bottom-up approach) being offset by biogenic CH<sub>4</sub> and N<sub>2</sub>O emissions, predominantly coming from the agricultural sectors. Emerging data sources and modeling capacities have helped achieve agreement between the top-down and bottom-up approaches, but sizable uncertainties remain in several flux terms. For example, the reported CO<sub>2</sub> flux from land use and land cover change varies from a net source of more than 300 Tg CO<sub>2</sub> yr<sup>−1</sup> to a net sink of ∼−700 Tg CO<sub>2</sub> yr<sup>−1</sup>. Although terrestrial ecosystems over East Asia is close to GHG neutral currently, curbing agricultural GHG emissions and additional afforestation and forest managements have the potential to transform the terrestrial ecosystems into a net GHG sink, which would help in realizing East Asian countries' ambitions to achieve climate neutrality.</p>","PeriodicalId":12729,"journal":{"name":"Global Biogeochemical Cycles","volume":null,"pages":null},"PeriodicalIF":5.2,"publicationDate":"2024-02-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139937345","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
The Arctic is experiencing dramatic climate-induced changes, which could have substantial consequences for nutrient export from land to streams and, thus, in-stream nutrient availability and composition. Arctic freshwater ecosystems are low-productive systems often limited by nitrogen (N) availability. Studying small streams is important due to their high abundance across the landscape, intimate connection to their catchments, high biogeochemical activity and high sensitivity to climate change. However, little information is available, especially in terms of N availability and composition (i.e., nitrate, ammonium, and dissolved organic nitrogen [DON]). We aimed to quantify N concentrations across small Arctic streams and explore the link between terrestrial vegetation and stream water N concentration. We conducted a literature study and extracted data from published articles, online databases, and unpublished field data. Out of 215 preselected articles, 20 met our criteria and contained 2,381 observations on stream water N concentrations in the Arctic. Data on DON was scarce: only 161 of the 2,381 observations contained DON data. We found that nitrate (NO3−), ammonium (NH4+) and DON ranged undetectable to 1,155, 547 and 1,587 μg N L−1, respectively. We found that sparsely vegetated areas had higher stream water N-concentrations, while barren areas and higher vegetated areas had lower stream water N-concentrations. This study provides fundamental knowledge on N availability in small streams across the Arctic, highlights data gaps and contributes to the basic knowledge needed for understanding and predicting future changes in N dynamics.
北极地区正在经历由气候引起的剧烈变化,这可能会对从陆地向溪流的营养物质输出产生重大影响,进而影响溪流中营养物质的可用性和组成。北极淡水生态系统是低生产力系统,通常受到氮(N)供应的限制。研究小溪流非常重要,因为它们在整个地形中数量众多,与集水区的联系密切,生物地球化学活性高,对气候变化非常敏感。然而,有关氮的可用性和组成(即硝酸盐、铵和溶解有机氮 [DON])的信息却很少。我们的目标是量化北极小溪的氮浓度,并探索陆地植被与溪水氮浓度之间的联系。我们进行了文献研究,并从已发表的文章、在线数据库和未发表的实地数据中提取了数据。在 215 篇预选文章中,有 20 篇符合我们的标准,其中包含 2,381 项关于北极地区溪水氮浓度的观测数据。有关 DON 的数据很少:2,381 个观测数据中只有 161 个包含 DON 数据。我们发现,硝酸盐 (NO3-)、铵 (NH4+) 和 DON 的含量范围分别从检测不到到 1,155, 547 和 1,587 μg N L-1 不等。我们发现,植被稀疏地区的溪水氮浓度较高,而贫瘠地区和植被较高地区的溪水氮浓度较低。这项研究提供了有关北极地区小溪流氮可用性的基础知识,突出了数据缺口,并为理解和预测未来氮动态变化提供了所需的基础知识。
{"title":"Stream Nitrogen Concentrations Across Arctic Vegetation Gradients","authors":"C. M. H. Holmboe, A. Pastor, T. Riis","doi":"10.1029/2023GB007840","DOIUrl":"https://doi.org/10.1029/2023GB007840","url":null,"abstract":"<p>The Arctic is experiencing dramatic climate-induced changes, which could have substantial consequences for nutrient export from land to streams and, thus, in-stream nutrient availability and composition. Arctic freshwater ecosystems are low-productive systems often limited by nitrogen (N) availability. Studying small streams is important due to their high abundance across the landscape, intimate connection to their catchments, high biogeochemical activity and high sensitivity to climate change. However, little information is available, especially in terms of N availability and composition (i.e., nitrate, ammonium, and dissolved organic nitrogen [DON]). We aimed to quantify N concentrations across small Arctic streams and explore the link between terrestrial vegetation and stream water N concentration. We conducted a literature study and extracted data from published articles, online databases, and unpublished field data. Out of 215 preselected articles, 20 met our criteria and contained 2,381 observations on stream water N concentrations in the Arctic. Data on DON was scarce: only 161 of the 2,381 observations contained DON data. We found that nitrate (NO<sub>3</sub><sup>−</sup>), ammonium (NH<sub>4</sub><sup>+</sup>) and DON ranged undetectable to 1,155, 547 and 1,587 μg N L<sup>−1</sup>, respectively. We found that sparsely vegetated areas had higher stream water N-concentrations, while barren areas and higher vegetated areas had lower stream water N-concentrations. This study provides fundamental knowledge on N availability in small streams across the Arctic, highlights data gaps and contributes to the basic knowledge needed for understanding and predicting future changes in N dynamics.</p>","PeriodicalId":12729,"journal":{"name":"Global Biogeochemical Cycles","volume":null,"pages":null},"PeriodicalIF":5.2,"publicationDate":"2024-02-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1029/2023GB007840","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139916730","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
This study explores the carbon stability in the Arctic permafrost following the sea-level transgression since the Last Glacial Maximum (LGM). The Arctic permafrost stores a significant amount of organic carbon sequestered as frozen particulate organic carbon, solid methane hydrate and free methane gas. Post-LGM sea-level transgression resulted in ocean water, which is up to 20°C warmer compared to the average annual air mass, inundating, and thawing the permafrost. This study develops a one-dimensional multiphase flow, multicomponent transport numerical model and apply it to investigate the coupled thermal, hydraulic, microbial, and chemical processes occurring in the thawing subsea permafrost. Results show that microbial methane is produced and vented to the seawater immediately upon the flooding of the Arctic continental shelves. This microbial methane is generated by the biodegradation of the previously frozen organic carbon. The maximum seabed methane flux is predicted in the shallow water where the sediment has been warmed up, but the remaining amount of organic carbon is still high. It is less likely to cause seabed methane emission by methane hydrate dissociation. Such a situation only happens when there is a very shallow (∼200 m depth) intra-permafrost methane hydrate, the occurrence of which is limited. This study provides insights into the limits of methane release from the ongoing flooding of the Arctic permafrost, which is critical to understand the role of the Arctic permafrost in the carbon cycle, ocean chemistry and climate change.
{"title":"Biodegradation of Ancient Organic Carbon Fuels Seabed Methane Emission at the Arctic Continental Shelves","authors":"Kehua You","doi":"10.1029/2023GB007999","DOIUrl":"https://doi.org/10.1029/2023GB007999","url":null,"abstract":"<p>This study explores the carbon stability in the Arctic permafrost following the sea-level transgression since the Last Glacial Maximum (LGM). The Arctic permafrost stores a significant amount of organic carbon sequestered as frozen particulate organic carbon, solid methane hydrate and free methane gas. Post-LGM sea-level transgression resulted in ocean water, which is up to 20°C warmer compared to the average annual air mass, inundating, and thawing the permafrost. This study develops a one-dimensional multiphase flow, multicomponent transport numerical model and apply it to investigate the coupled thermal, hydraulic, microbial, and chemical processes occurring in the thawing subsea permafrost. Results show that microbial methane is produced and vented to the seawater immediately upon the flooding of the Arctic continental shelves. This microbial methane is generated by the biodegradation of the previously frozen organic carbon. The maximum seabed methane flux is predicted in the shallow water where the sediment has been warmed up, but the remaining amount of organic carbon is still high. It is less likely to cause seabed methane emission by methane hydrate dissociation. Such a situation only happens when there is a very shallow (∼200 m depth) intra-permafrost methane hydrate, the occurrence of which is limited. This study provides insights into the limits of methane release from the ongoing flooding of the Arctic permafrost, which is critical to understand the role of the Arctic permafrost in the carbon cycle, ocean chemistry and climate change.</p>","PeriodicalId":12729,"journal":{"name":"Global Biogeochemical Cycles","volume":null,"pages":null},"PeriodicalIF":5.2,"publicationDate":"2024-02-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139750122","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Rivers and streams play an important role within the global carbon cycle, in part through emissions of carbon dioxide (CO2) to the atmosphere. However, the sources of this CO2 and their spatiotemporal variability are difficult to constrain. Recent work has highlighted the role of carbonate buffering reactions that may serve as a source of CO2 in high alkalinity systems. In this study, we seek to develop a quantitative framework for the role of carbonate buffering in the fluxes and spatiotemporal patterns of CO2 and the stable and radio- isotope composition of dissolved inorganic carbon (DIC). We incorporate DIC speciation calculations of carbon isotopologues into a stream network CO2 model and perform a series of simulations, ranging from the degassing of a groundwater seep to a hydrologically-coupled 5th-order stream network. We find that carbonate buffering reactions contribute >60% of emissions in high-alkalinity, moderate groundwater-CO2 environments. However, atmosphere equilibration timescales of CO2 are minimally affected, which contradicts hypotheses that carbonate buffering maintains high CO2 across Strahler orders in high alkalinity systems. In contrast, alkalinity dramatically increases isotope equilibration timescales, which acts to decouple CO2 and DIC variations from the isotopic composition even under low alkalinity. This significantly complicates a common method for carbon source identification. Based on similar impacts on atmospheric equilibration for stable and radio- carbon isotopologues, we develop a quantitative method for partitioning groundwater and stream corridor carbon sources in carbonate-dominated watersheds. Together, these results provide a framework to guide fieldwork and interpretations of stream network CO2 patterns across variable alkalinities.
河流和溪流在全球碳循环中扮演着重要角色,部分原因是向大气排放了二氧化碳(CO2)。然而,这些二氧化碳的来源及其时空变化难以确定。最近的研究强调了碳酸盐缓冲反应的作用,它可能是高碱度系统中的二氧化碳来源。在本研究中,我们试图为碳酸盐缓冲作用在二氧化碳通量和时空模式中的作用以及溶解无机碳(DIC)的稳定和放射性同位素组成建立一个定量框架。我们将碳同位素的 DIC 分类计算纳入溪流网络二氧化碳模型,并进行了从地下水渗漏脱气到水文耦合五阶溪流网络等一系列模拟。我们发现,在高碱度、中度地下水-CO2 环境中,碳酸盐缓冲反应占排放量的 60%。然而,大气中 CO2 的平衡时间尺度受到的影响很小,这与碳酸盐缓冲作用在高碱度系统中保持高 CO2 跨斯特雷勒阶的假设相矛盾。相反,碱度会显著增加同位素平衡时间尺度,从而使二氧化碳和 DIC 的变化与同位素组成脱钩,即使在低碱度条件下也是如此。这大大增加了碳源识别的常用方法的复杂性。基于稳定碳和放射性碳同位素对大气平衡的类似影响,我们开发了一种定量方法,用于划分碳酸盐主导流域的地下水和溪流走廊碳源。这些结果为指导野外工作和解释不同碱度的溪流网络二氧化碳模式提供了一个框架。
{"title":"Impacts of Carbonate Buffering on Atmospheric Equilibration of CO2, δ13CDIC, and Δ14CDIC in Rivers and Streams","authors":"Matthew J. Winnick, Brian Saccardi","doi":"10.1029/2023GB007860","DOIUrl":"https://doi.org/10.1029/2023GB007860","url":null,"abstract":"<p>Rivers and streams play an important role within the global carbon cycle, in part through emissions of carbon dioxide (CO<sub>2</sub>) to the atmosphere. However, the sources of this CO<sub>2</sub> and their spatiotemporal variability are difficult to constrain. Recent work has highlighted the role of carbonate buffering reactions that may serve as a source of CO<sub>2</sub> in high alkalinity systems. In this study, we seek to develop a quantitative framework for the role of carbonate buffering in the fluxes and spatiotemporal patterns of CO<sub>2</sub> and the stable and radio- isotope composition of dissolved inorganic carbon (DIC). We incorporate DIC speciation calculations of carbon isotopologues into a stream network CO<sub>2</sub> model and perform a series of simulations, ranging from the degassing of a groundwater seep to a hydrologically-coupled 5th-order stream network. We find that carbonate buffering reactions contribute >60% of emissions in high-alkalinity, moderate groundwater-CO<sub>2</sub> environments. However, atmosphere equilibration timescales of CO<sub>2</sub> are minimally affected, which contradicts hypotheses that carbonate buffering maintains high CO<sub>2</sub> across Strahler orders in high alkalinity systems. In contrast, alkalinity dramatically increases isotope equilibration timescales, which acts to decouple CO<sub>2</sub> and DIC variations from the isotopic composition even under low alkalinity. This significantly complicates a common method for carbon source identification. Based on similar impacts on atmospheric equilibration for stable and radio- carbon isotopologues, we develop a quantitative method for partitioning groundwater and stream corridor carbon sources in carbonate-dominated watersheds. Together, these results provide a framework to guide fieldwork and interpretations of stream network CO<sub>2</sub> patterns across variable alkalinities.</p>","PeriodicalId":12729,"journal":{"name":"Global Biogeochemical Cycles","volume":null,"pages":null},"PeriodicalIF":5.2,"publicationDate":"2024-02-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1029/2023GB007860","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139719818","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Florian Scholz, Dalton S. Hardisty, Andrew W. Dale
Iodine cycling in the ocean is closely linked to productivity, organic carbon export, and oxygenation. However, iodine sources and sinks at the seafloor are poorly constrained, which limits the applicability of iodine as a biogeochemical tracer. We present pore water and solid phase iodine data for sediment cores from the Peruvian continental margin, which cover a range of bottom water oxygen concentrations, organic carbon rain rates and sedimentation rates. By applying a numerical reaction-transport model, we evaluate how these parameters determine benthic iodine fluxes and sedimentary iodine-to-organic carbon ratios (I:Corg) in the paleo-record. Iodine is delivered to the sediment with organic material and released into the pore water as iodide (I−) during early diagenesis. Under anoxic conditions in the bottom water, most of the iodine delivered is recycled, which can explain the presence of excess dissolved iodine in near-shore anoxic seawater. According to our model, the benthic I− efflux in anoxic areas is mainly determined by the organic carbon rain rate. Under oxic conditions, pore water dissolved I− is oxidized and precipitated at the sediment surface. Much of the precipitated iodine re-dissolves during early diagenesis and only a fraction is buried. Particulate iodine burial efficiency and I:Corg burial ratios do increase with bottom water oxygen. However, multiple combinations of bottom water oxygen, organic carbon rain rate and sedimentation rate can lead to identical I:Corg, which limits the utility of I:Corg as a quantitative oxygenation proxy. Our findings may help to better constrain the ocean's iodine mass balance, both today and in the geological past.
{"title":"Early Diagenetic Controls on Sedimentary Iodine Release and Iodine-To-Organic Carbon Ratios in the Paleo-Record","authors":"Florian Scholz, Dalton S. Hardisty, Andrew W. Dale","doi":"10.1029/2023GB007919","DOIUrl":"https://doi.org/10.1029/2023GB007919","url":null,"abstract":"<p>Iodine cycling in the ocean is closely linked to productivity, organic carbon export, and oxygenation. However, iodine sources and sinks at the seafloor are poorly constrained, which limits the applicability of iodine as a biogeochemical tracer. We present pore water and solid phase iodine data for sediment cores from the Peruvian continental margin, which cover a range of bottom water oxygen concentrations, organic carbon rain rates and sedimentation rates. By applying a numerical reaction-transport model, we evaluate how these parameters determine benthic iodine fluxes and sedimentary iodine-to-organic carbon ratios (I:C<sub>org</sub>) in the paleo-record. Iodine is delivered to the sediment with organic material and released into the pore water as iodide (I<sup>−</sup>) during early diagenesis. Under anoxic conditions in the bottom water, most of the iodine delivered is recycled, which can explain the presence of excess dissolved iodine in near-shore anoxic seawater. According to our model, the benthic I<sup>−</sup> efflux in anoxic areas is mainly determined by the organic carbon rain rate. Under oxic conditions, pore water dissolved I<sup>−</sup> is oxidized and precipitated at the sediment surface. Much of the precipitated iodine re-dissolves during early diagenesis and only a fraction is buried. Particulate iodine burial efficiency and I:C<sub>org</sub> burial ratios do increase with bottom water oxygen. However, multiple combinations of bottom water oxygen, organic carbon rain rate and sedimentation rate can lead to identical I:C<sub>org</sub>, which limits the utility of I:C<sub>org</sub> as a quantitative oxygenation proxy. Our findings may help to better constrain the ocean's iodine mass balance, both today and in the geological past.</p>","PeriodicalId":12729,"journal":{"name":"Global Biogeochemical Cycles","volume":null,"pages":null},"PeriodicalIF":5.2,"publicationDate":"2024-02-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1029/2023GB007919","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139682926","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
The ocean's biological carbon pump (BCP) affects the Earth's climate by sequestering CO2 away from the atmosphere for decades to millennia. One primary control on the amount of carbon sequestered by the biological pump is air-sea CO2 disequilibrium, which is controlled by the rate of air-sea CO2 exchange and the residence time of CO2 in surface waters. Here, we use a data-assimilated model of the soft tissue BCP to quantify carbon sequestration inventories and time scales from remineralization in the water column to equilibration with the atmosphere. We find that air-sea CO2 disequilibrium enhances the global biogenic carbon inventory by ∼35% and its sequestration time by ∼70 years compared to identical calculations made assuming instantaneous air-sea CO2 exchange. Locally, the greatest enhancement occurs in the subpolar Southern Ocean, where air-sea disequilibrium increases sequestration times by up to 600 years and the biogenic dissolved inorganic carbon inventory by >100% in the upper ocean. Contrastingly, in deep-water formation regions of the North Atlantic and Antarctic margins, where biological production creates undersaturated surface waters which are subducted before fully equilibrating with the atmosphere, air-sea CO2 disequilibrium decreases the depth-integrated sequestration inventory by up to ∼150%. The global enhancement of carbon sequestration by air-sea disequilibrium is particularly important for carbon respired in deep waters that upwell in the Southern Ocean. These results highlight the importance of accounting for air-sea CO2 disequilibrium when evaluating carbon sequestration by the biological pump and for assessing the efficacy of ocean-based CO2 removal methods.
{"title":"The Influence of Air-Sea CO2 Disequilibrium on Carbon Sequestration by the Ocean's Biological Pump","authors":"Michael Nowicki, Tim DeVries, David A. Siegel","doi":"10.1029/2023GB007880","DOIUrl":"10.1029/2023GB007880","url":null,"abstract":"<p>The ocean's biological carbon pump (BCP) affects the Earth's climate by sequestering CO<sub>2</sub> away from the atmosphere for decades to millennia. One primary control on the amount of carbon sequestered by the biological pump is air-sea CO<sub>2</sub> disequilibrium, which is controlled by the rate of air-sea CO<sub>2</sub> exchange and the residence time of CO<sub>2</sub> in surface waters. Here, we use a data-assimilated model of the soft tissue BCP to quantify carbon sequestration inventories and time scales from remineralization in the water column to equilibration with the atmosphere. We find that air-sea CO<sub>2</sub> disequilibrium enhances the global biogenic carbon inventory by ∼35% and its sequestration time by ∼70 years compared to identical calculations made assuming instantaneous air-sea CO<sub>2</sub> exchange. Locally, the greatest enhancement occurs in the subpolar Southern Ocean, where air-sea disequilibrium increases sequestration times by up to 600 years and the biogenic dissolved inorganic carbon inventory by >100% in the upper ocean. Contrastingly, in deep-water formation regions of the North Atlantic and Antarctic margins, where biological production creates undersaturated surface waters which are subducted before fully equilibrating with the atmosphere, air-sea CO<sub>2</sub> disequilibrium decreases the depth-integrated sequestration inventory by up to ∼150%. The global enhancement of carbon sequestration by air-sea disequilibrium is particularly important for carbon respired in deep waters that upwell in the Southern Ocean. These results highlight the importance of accounting for air-sea CO<sub>2</sub> disequilibrium when evaluating carbon sequestration by the biological pump and for assessing the efficacy of ocean-based CO<sub>2</sub> removal methods.</p>","PeriodicalId":12729,"journal":{"name":"Global Biogeochemical Cycles","volume":null,"pages":null},"PeriodicalIF":5.2,"publicationDate":"2024-01-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1029/2023GB007880","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139579386","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
L. Resplandy, A. Hogikyan, J. D. Müller, R. G. Najjar, H. W. Bange, D. Bianchi, T. Weber, W.-J. Cai, S. C. Doney, K. Fennel, M. Gehlen, J. Hauck, F. Lacroix, P. Landschützer, C. Le Quéré, A. Roobaert, J. Schwinger, S. Berthet, L. Bopp, T. T. T. Chau, M. Dai, N. Gruber, T. Ilyina, A. Kock, M. Manizza, Z. Lachkar, G. G. Laruelle, E. Liao, I. D. Lima, C. Nissen, C. Rödenbeck, R. Séférian, K. Toyama, H. Tsujino, P. Regnier
The coastal ocean contributes to regulating atmospheric greenhouse gas concentrations by taking up carbon dioxide (CO2) and releasing nitrous oxide (N2O) and methane (CH4). In this second phase of the Regional Carbon Cycle Assessment and Processes (RECCAP2), we quantify global coastal ocean fluxes of CO2, N2O and CH4 using an ensemble of global gap-filled observation-based products and ocean biogeochemical models. The global coastal ocean is a net sink of CO2 in both observational products and models, but the magnitude of the median net global coastal uptake is ∼60% larger in models (−0.72 vs. −0.44 PgC year−1, 1998–2018, coastal ocean extending to 300 km offshore or 1,000 m isobath with area of 77 million km2). We attribute most of this model-product difference to the seasonality in sea surface CO2 partial pressure at mid- and high-latitudes, where models simulate stronger winter CO2 uptake. The coastal ocean CO2 sink has increased in the past decades but the available time-resolving observation-based products and models show large discrepancies in the magnitude of this increase. The global coastal ocean is a major source of N2O (+0.70 PgCO2-e year−1 in observational product and +0.54 PgCO2-e year−1 in model median) and CH4 (+0.21 PgCO2-e year−1 in observational product), which offsets a substantial proportion of the coastal CO2 uptake in the net radiative balance (30%–60% in CO2-equivalents), highlighting the importance of considering the three greenhouse gases when examining the influence of the coastal ocean on climate.
{"title":"A Synthesis of Global Coastal Ocean Greenhouse Gas Fluxes","authors":"L. Resplandy, A. Hogikyan, J. D. Müller, R. G. Najjar, H. W. Bange, D. Bianchi, T. Weber, W.-J. Cai, S. C. Doney, K. Fennel, M. Gehlen, J. Hauck, F. Lacroix, P. Landschützer, C. Le Quéré, A. Roobaert, J. Schwinger, S. Berthet, L. Bopp, T. T. T. Chau, M. Dai, N. Gruber, T. Ilyina, A. Kock, M. Manizza, Z. Lachkar, G. G. Laruelle, E. Liao, I. D. Lima, C. Nissen, C. Rödenbeck, R. Séférian, K. Toyama, H. Tsujino, P. Regnier","doi":"10.1029/2023GB007803","DOIUrl":"https://doi.org/10.1029/2023GB007803","url":null,"abstract":"<p>The coastal ocean contributes to regulating atmospheric greenhouse gas concentrations by taking up carbon dioxide (CO<sub>2</sub>) and releasing nitrous oxide (N<sub>2</sub>O) and methane (CH<sub>4</sub>). In this second phase of the Regional Carbon Cycle Assessment and Processes (RECCAP2), we quantify global coastal ocean fluxes of CO<sub>2</sub>, N<sub>2</sub>O and CH<sub>4</sub> using an ensemble of global gap-filled observation-based products and ocean biogeochemical models. The global coastal ocean is a net sink of CO<sub>2</sub> in both observational products and models, but the magnitude of the median net global coastal uptake is ∼60% larger in models (−0.72 vs. −0.44 PgC year<sup>−1</sup>, 1998–2018, coastal ocean extending to 300 km offshore or 1,000 m isobath with area of 77 million km<sup>2</sup>). We attribute most of this model-product difference to the seasonality in sea surface CO<sub>2</sub> partial pressure at mid- and high-latitudes, where models simulate stronger winter CO<sub>2</sub> uptake. The coastal ocean CO<sub>2</sub> sink has increased in the past decades but the available time-resolving observation-based products and models show large discrepancies in the magnitude of this increase. The global coastal ocean is a major source of N<sub>2</sub>O (+0.70 PgCO<sub>2</sub>-e year<sup>−1</sup> in observational product and +0.54 PgCO<sub>2</sub>-e year<sup>−1</sup> in model median) and CH<sub>4</sub> (+0.21 PgCO<sub>2</sub>-e year<sup>−1</sup> in observational product), which offsets a substantial proportion of the coastal CO<sub>2</sub> uptake in the net radiative balance (30%–60% in CO<sub>2</sub>-equivalents), highlighting the importance of considering the three greenhouse gases when examining the influence of the coastal ocean on climate.</p>","PeriodicalId":12729,"journal":{"name":"Global Biogeochemical Cycles","volume":null,"pages":null},"PeriodicalIF":5.2,"publicationDate":"2024-01-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1029/2023GB007803","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139504618","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Vinícius J. Amaral, Phoebe J. Lam, Olivier Marchal, Jennifer A. Kenyon
Understanding particle cycling processes in the ocean is critical for predicting the response of the biological carbon pump to external perturbations. Here, measurements of particulate organic carbon (POC) concentration in two size fractions (1–51 and >51 μm) from GEOTRACES Pacific meridional transect GP15 are combined with a POC cycling model to estimate rates of POC production, (dis)aggregation, sinking, remineralization, and vertical transport mediated by migrating zooplankton, in the euphotic zone (EZ) and upper mesopelagic zone (UMZ) of distinct environments. We find coherent variations in POC cycling parameters and fluxes throughout the transect. Thus, the settling speed of POC in the >51 μm fraction increased with depth in the UMZ, presumably due to higher particle densities at depth. The settling flux of total POC (>1 μm) out of the EZ was positively correlated with primary production integrated over the EZ; the highest export occurred in the subarctic gyre while the lowest occurred in the subtropical gyres. The ratio of POC settling flux to integrated primary production was low (<5%) along GP15, which suggests an efficient recycling of POC in the EZ in all trophic regimes. Specific rates of POC remineralization did not show clear variations with temperature or dissolved oxygen concentration, that is, POC recycling was apparently controlled by other factors such as microbial colonization and substrate lability. Particle cohesiveness, as approximated by the second-order rate constant for particle aggregation, was negatively correlated with trophic regime: particles appeared more cohesive in low-productivity regions than in high-productivity regions.
{"title":"Cycling Rates of Particulate Organic Carbon Along the GEOTRACES Pacific Meridional Transect GP15","authors":"Vinícius J. Amaral, Phoebe J. Lam, Olivier Marchal, Jennifer A. Kenyon","doi":"10.1029/2023GB007940","DOIUrl":"https://doi.org/10.1029/2023GB007940","url":null,"abstract":"<p>Understanding particle cycling processes in the ocean is critical for predicting the response of the biological carbon pump to external perturbations. Here, measurements of particulate organic carbon (POC) concentration in two size fractions (1–51 and >51 μm) from GEOTRACES Pacific meridional transect GP15 are combined with a POC cycling model to estimate rates of POC production, (dis)aggregation, sinking, remineralization, and vertical transport mediated by migrating zooplankton, in the euphotic zone (EZ) and upper mesopelagic zone (UMZ) of distinct environments. We find coherent variations in POC cycling parameters and fluxes throughout the transect. Thus, the settling speed of POC in the >51 μm fraction increased with depth in the UMZ, presumably due to higher particle densities at depth. The settling flux of total POC (>1 μm) out of the EZ was positively correlated with primary production integrated over the EZ; the highest export occurred in the subarctic gyre while the lowest occurred in the subtropical gyres. The ratio of POC settling flux to integrated primary production was low (<5%) along GP15, which suggests an efficient recycling of POC in the EZ in all trophic regimes. Specific rates of POC remineralization did not show clear variations with temperature or dissolved oxygen concentration, that is, POC recycling was apparently controlled by other factors such as microbial colonization and substrate lability. Particle cohesiveness, as approximated by the second-order rate constant for particle aggregation, was negatively correlated with trophic regime: particles appeared more cohesive in low-productivity regions than in high-productivity regions.</p>","PeriodicalId":12729,"journal":{"name":"Global Biogeochemical Cycles","volume":null,"pages":null},"PeriodicalIF":5.2,"publicationDate":"2024-01-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1029/2023GB007940","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139473873","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Luca Stirnimann, Thomas G. Bornman, Heather J. Forrer, Joshua Mirkin, Thomas J. Ryan-Keogh, Raquel F. Flynn, Rosemary A. Dorrington, Hans M. Verheye, Sarah E. Fawcett
The Southern Ocean accounts for ∼30% of the ocean's CO2 sink, partly due to its biological pump that transfers surface-produced organic carbon to deeper waters. To estimate large-scale Southern Ocean carbon export potential and characterize its drivers, we measured the carbon and nitrogen isotope ratios of surface suspended particulate matter (δ13CSPM, δ15NSPM) for samples collected in summer 2016/2017 during the Antarctic Circumnavigation Expedition (364 stations). Concurrent measurements of phytoplankton community composition revealed the dominance of large diatoms in the Antarctic and nano-phytoplankton (mainly haptophytes) in open Subantarctic waters. As expected, δ13CSPM was strongly dependent on pCO2, with local deviations in this relationship explained by phytoplankton community dynamics. δ15NSPM reflected the nitrogen sources consumed by phytoplankton, with higher inferred nitrate (versus recycled ammonium) dependence generally coinciding with higher micro-phytoplankton abundances. Using δ15NSPM and a two-endmember isotope mixing model, we quantified the extent of nitrate- versus ammonium-supported growth, which yields a measure of carbon export potential. We estimate that across the Southern Ocean, 41 ± 29% of the surface-produced organic carbon was potentially exported below the seasonal mixed layer during the growth season, with maximum export potential (50%–99%) occurring in the Antarctic Circumpolar Current's southern Boundary Zone and near the (Sub)Antarctic islands, reaching a minimum in the Subtropical Zone (<33%). Alongside iron, phytoplankton community composition emerged as an important driver of the Southern Ocean's biological pump, with large diatoms dominating regions characterized by high nitrate dependence and elevated carbon export potential and smaller, mainly non-diatom taxa proliferating in waters where recycled ammonium supported most productivity.
{"title":"A Circum-Antarctic Plankton Isoscape: Carbon Export Potential Across the Summertime Southern Ocean","authors":"Luca Stirnimann, Thomas G. Bornman, Heather J. Forrer, Joshua Mirkin, Thomas J. Ryan-Keogh, Raquel F. Flynn, Rosemary A. Dorrington, Hans M. Verheye, Sarah E. Fawcett","doi":"10.1029/2023GB007808","DOIUrl":"https://doi.org/10.1029/2023GB007808","url":null,"abstract":"<p>The Southern Ocean accounts for ∼30% of the ocean's CO<sub>2</sub> sink, partly due to its biological pump that transfers surface-produced organic carbon to deeper waters. To estimate large-scale Southern Ocean carbon export potential and characterize its drivers, we measured the carbon and nitrogen isotope ratios of surface suspended particulate matter (δ<sup>13</sup>C<sub>SPM</sub>, δ<sup>15</sup>N<sub>SPM</sub>) for samples collected in summer 2016/2017 during the Antarctic Circumnavigation Expedition (364 stations). Concurrent measurements of phytoplankton community composition revealed the dominance of large diatoms in the Antarctic and nano-phytoplankton (mainly haptophytes) in open Subantarctic waters. As expected, δ<sup>13</sup>C<sub>SPM</sub> was strongly dependent on pCO<sub>2</sub>, with local deviations in this relationship explained by phytoplankton community dynamics. δ<sup>15</sup>N<sub>SPM</sub> reflected the nitrogen sources consumed by phytoplankton, with higher inferred nitrate (versus recycled ammonium) dependence generally coinciding with higher micro-phytoplankton abundances. Using δ<sup>15</sup>N<sub>SPM</sub> and a two-endmember isotope mixing model, we quantified the extent of nitrate- versus ammonium-supported growth, which yields a measure of carbon export potential. We estimate that across the Southern Ocean, 41 ± 29% of the surface-produced organic carbon was potentially exported below the seasonal mixed layer during the growth season, with maximum export potential (50%–99%) occurring in the Antarctic Circumpolar Current's southern Boundary Zone and near the (Sub)Antarctic islands, reaching a minimum in the Subtropical Zone (<33%). Alongside iron, phytoplankton community composition emerged as an important driver of the Southern Ocean's biological pump, with large diatoms dominating regions characterized by high nitrate dependence and elevated carbon export potential and smaller, mainly non-diatom taxa proliferating in waters where recycled ammonium supported most productivity.</p>","PeriodicalId":12729,"journal":{"name":"Global Biogeochemical Cycles","volume":null,"pages":null},"PeriodicalIF":5.2,"publicationDate":"2024-01-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1029/2023GB007808","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139435279","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}